This article provides an example of how to implement recursion algorithm to copy a whole directory (including its nested child directories and files) to a new location in the file system. Here’s the algorithm we would like to suggest:

1. 1. List content of the current directory.
   2. For each item in the current directory:
   • • If the item is a directory:
       • Create the directory in the new location.
       • Copy this directory by repeating the steps 1, 2, and 3 (At this point the function will call itself, hence the recursion).
     • If the item is a file, copy the file to the new location.

3. Return if the current directory is empty or if the last item is traversed.

We will implement the copy algorithm above in a utility class for the sake of reusability. Here’s structure of the utility class:

public class CopyUtil {

	// utility method which is exposed to the outside
	public static void copyDirectory(File sourceDir, File destDir)
			throws IOException {
		// checks arguments...
		// call copyDirectoryImpl()
	}

	// implementation of copy directory method
	private static void copyDirectoryImpl(File sourceDir, File destDir)
			throws IOException {
		// implements the recursion algorithm above...
		// calls copySingleFile() method
	}

	// copy a file
	private static void copySingleFile(File sourceFile, File destFile)
			throws IOException {
		// code to copy a file to another location
	}
}

Code of the copyDirectory() method:

/**
 * Copy a whole directory to another location.
 * @param sourceDir a File object represents the source directory
 * @param destDir a File object represents the destination directory
 * @throws IOException thrown if IO error occurred.
 */
public static void copyDirectory(File sourceDir, File destDir)
		throws IOException {
	// creates the destination directory if it does not exist
	if (!destDir.exists()) {
		destDir.mkdirs();
	}

	// throws exception if the source does not exist
	if (!sourceDir.exists()) {
		throw new IllegalArgumentException("sourceDir does not exist");
	}

	// throws exception if the arguments are not directories
	if (sourceDir.isFile() || destDir.isFile()) {
		throw new IllegalArgumentException(
				"Either sourceDir or destDir is not a directory");
	}

	copyDirectoryImpl(sourceDir, destDir);
}

Code of the copyDirectoryImpl() method:

/**
 * Internal implementation of the copy method.
 * @param sourceDir a File object represents the source directory
 * @param destDir a File object represents the destination directory
 * @throws IOException thrown if IO error occurred.
 */
private static void copyDirectoryImpl(File sourceDir, File destDir)
		throws IOException {
	File[] items = sourceDir.listFiles();
	if (items != null && items.length > 0) {
		for (File anItem : items) {
			if (anItem.isDirectory()) {
				// create the directory in the destination
				File newDir = new File(destDir, anItem.getName());
				System.out.println("CREATED DIR: "
						+ newDir.getAbsolutePath());
				newDir.mkdir();

				// copy the directory (recursive call)
				copyDirectory(anItem, newDir);
			} else {
				// copy the file
				File destFile = new File(destDir, anItem.getName());
				copySingleFile(anItem, destFile);
			}
		}
	}
}

Code of the copySingleFile() method:

/**
 * Copy a file from a location to another
 * @param sourceFile a File object represents the source file
 * @param destFile a File object represents the destination file
 * @throws IOException thrown if IO error occurred.
 */
private static void copySingleFile(File sourceFile, File destFile)
		throws IOException {
	System.out.println("COPY FILE: " + sourceFile.getAbsolutePath()
			+ " TO: " + destFile.getAbsolutePath());
	if (!destFile.exists()) {
		destFile.createNewFile();
	}

	FileChannel sourceChannel = null;
	FileChannel destChannel = null;

	try {
		sourceChannel = new FileInputStream(sourceFile).getChannel();
		destChannel = new FileOutputStream(destFile).getChannel();
		sourceChannel.transferTo(0, sourceChannel.size(), destChannel);
	} finally {
		if (sourceChannel != null) {
			sourceChannel.close();
		}
		if (destChannel != null) {
			destChannel.close();
		}
	}
}

To test the utility class, create a program as follows:

import java.io.File;
import java.io.IOException;

/**
 * This program tests the CopyUtil class for copying a whole directory.
 * @author www.codejava.net
 *
 */
public class CopyDirectoryTest {

	public static void main(String[] args) {
		File sourceDir = new File("E:/TestCopy");
		File destDir = new File("D:/Copy");

		try {
			CopyUtil.copyDirectory(sourceDir, destDir);
		} catch (IOException ex) {
			ex.printStackTrace();
		}
	}
}

This program will copy content of the directory E:/TestCopy to the directory D:/Copy, supposing the E:/TestCopy directory has the following structure:

 

Then the test program will output the following:

 

Related File IO Tutorials:

• Calculate total files, sub directories and size of a directory
• How to list files and directories in a directory
• List files and directories recursively in a directory in Java
• How to rename/move file or directory in Java

 

Other Java File IO Tutorials:

• How to Read and Write Text File in Java
• How to Read and Write Binary Files in Java
• Java IO - Common File and Directory Operations Examples
• Java Serialization Basic Example
• Understanding Java Externalization with Examples
• How to execute Operating System Commands in Java
• 3 ways for reading user's input from console in Java
• File change notification example with Watch Service API
• Java Scanner Tutorial and Code Examples